Home PageAstronomy ArticlesStars PageAstronomy Links

Year's Earliest Sunset not on Year's Shortest Day

This may come as a big surprise, but the earliest sunset of the year doesn't fall on the same day as the December 21st solstice, the shortest day of the year in the Northern Hemisphere. In Denver, Colorado, for instance, the earliest sunset comes on December 7, two weeks before the winter solstice. At 40 degrees latitude, Denver represents the middle latitudes of the continental United States.

At latitudes appreciably south of Denver, the earliest sunset of the year comes before Dec. 7; north of Denver, it comes after. At Honolulu, Hawaii (21.6 degrees north latitude), the earliest sunset happens around November 25. Going northward, to Circle, Alaska (65.8 degrees north latitude), the earliest sunset occurs on December 19, quite close to the winter solstice.

Earliest Equatorial Sunset

Let's go to the equator (0 degrees latitude), where the daylight hours are virtually the same for every single day of the year. There, the earliest sunset of the year falls on November 3. The reader may object, "This makes no sense. At the equator, where the daylight hours are the same every day of the year, wouldn't it follow that the sunset would take place at the same time every day?"

The answer would be yes, if in addtion, noon happened at the same time for every day of the year. But it doesn't. The earliest noon of the year occurs on or near November 3. Therefore, since the earliest noon takes place in early November, the earliest sunset (and the earliest sunrise) has to be on this same date at the equator, where daylight hours remain constant throughout the year.

Definition of Noon

A definition of noon may be in order. By noon, we mean midday, the instant when the sun reaches its highest point in the sky for the day. We call this "solar noon," to distinguish it from "clock noon." The clock presumes the sun returns to its noontime position in the sky in exact periods of 24 hours. However, the period of the day as measured from solar noon to solar noon rarely measures exactly 24 hours.

Discrepancy between Clock & Sun

It's the discrepancy between the clock and sun that causes the day of earliest sunset to arrive before the winter solstice, the shortest day of the year. I should emphasize by "shortest" day, I mean shortest period of daylight. For several months after the day of the earliest solar noon (as read by the clock), the day as measured from solar noon to solar noon EXCEEDS 24 hours. Not by a lot, mind you, but the discrepancy accumulates. On the December solstice, solar noon comes some 14 to 15 minutes later (by the clock) than it does on November 3.

Therefore, here's the story for Quito, Equador, a city residing on the Earth's equator:

Quito, Equador

DateSunriseSolar NoonSunset
Nov. 35:54 a.m.11:58 a.m.6:01 p.m.
Dec. 216:08 a.m.12:12 p.m.6:16 p.m.

Going North of the Equator

As we go north of the equator, the daylight hours get shorter daily as we approach the winter solstice. The farther north you live, the daily loss in sunlight is all the more accentuated. At different latitudes, the earliest sunset occurs on different dates, but it all hinges on the discrepancy between clock noon and solar noon.

Near the time of the winter solstice, the daily variation in daylight hours becomes very small -- so small, in fact, that the itty-bitty lessening of the daylight hours can't overcome the advancing clock time of solar noon and sunset. At farther northern latitudes, the greater variation in daylight hours holds off the date of the earliest sunset, assuring a closer correlation between the earliest sunset and the winter solstice.

A Tale of Three Cities

The tables below give the sunrise, solar noon and sunset times for Honolulu, Hawaii; Denver, Colorado; and Circle, Alaska. The bold inscription refers to the date and time of the earliest sunset. If you wish to know the earliest sunset for your locality, try the almanacs at Old Farmer's Almanac or the US Naval Observatory. Click here for a printable monthly calendar. For another article relating to the earliest sunset, I invite you to read The Equation of Time.

Honolulu, Hawaii

DateSunriseSolar NoonSunsetDaylight Hours
Nov. 36:35 a.m.12:15 p.m.5:55 p.m.11 hrs. 20 min.
Nov. 256:49 a.m.12:18 p.m.5:48 p.m.10 hrs. 59 min.
Dec. 217:04 a.m.12:30 p.m.5:55 p.m.10 hrs. 51 min.

Denver, Colorado

DateSunriseSolar NoonSunsetDaylight Hours
Nov. 36:31 a.m.11:43 a.m.4:56 p.m.10 hrs. 25 min.
Dec. 77:07 a.m.11:51 a.m.4:35 p.m.9 hrs. 28 min.
Dec. 217:17 a.m.11:58 a.m.4:39 p.m9 hrs. 22 min.

Circle, Alaska

DateSunriseSolar NoonSunsetDaylight Hours
Nov. 38:38 a.m.12:20 p.m.4:00 p.m.7 hrs. 22 min.
Dec. 1911:05 a.m.12:33 p.m.2:02 p.m.2 hrs. 57 min.
Dec. 2111:06 a.m.12:34 p.m.2:03 p.m.2 hrs. 57 min.

Next month, we'll explore the year's latest sunrise . . .

copyright 2006 by Bruce McClure

November 2006 Feature * January 2007 Feature